Abstract: Recent paleontological and neontological studies on feathers and feather-like integumentary structures have improved greatly our understanding of the origin and early evolution of feathers. New observations on some non-avian dinosaur specimens preserving integumentary structures, in combination with recent paleontological and neontological data, provide additional insights into this important evolutionary issue. Five major morphogenesis events are inferred to have occurred sequentially early in feather evolution before the origin of the Aves, and they are: 1) appearance of filamentous and tubular morphology, 2) formation of follicle and barb ridges, 3) appearance of rachis, 4) appearance of planar form, and 5) formation of pennaceous barbules. These events produce several morphotypes of feathers that are common among non-avian archosaurs but are probably lost later in avian evolution, and they also produced several morphotypes of feathers that are nearly identical or identical to those of modern birds. While feathers of non-avian dinosaurs exhibit many unique features of modern feathers, some of them also possess striking features unknown in modern feathers. Several models of evolutionary origin of feathers based on developmental data suggest that the origin of feathers is a completely innovative event and the first feathers have nothing to do with reptilian scales. We believe, however, that the defining features of modern feathers might have evolved in an incremental manner rather than in a sudden way. Consequently, an evolutionary model characteristic of both transformation and innovation is more acceptable for feather evolution. The function of the first feather is inferred to be neither related to flight nor to insulation. Display or heat dissipation, among others, remains viable hypotheses for initial function of feathers. An integrative study is promising to provide much new insights into the origin of feathers.

摘要： 近年来关于羽毛和羽状皮肤衍生物的研究极大促进了我们对羽毛起源与早期演化的理解。结合最新的古生物学与今生物学资料，对一些保存了皮肤衍生物的非鸟恐龙标本进行观察研究，为这个重要的进化问题提供了新见解。推测羽毛的演化在鸟类起源之前就以下列顺序完成了5个主要的形态发生事件：1) 丝状和管状结构的出现；2) 羽囊及羽枝脊形成；3) 羽轴的发生；4) 羽平面的形成；5) 羽状羽小支的产生。这些演化事件形成了多种曾存在于各类非鸟初龙类中的羽毛形态，但这些形态在鸟类演化过程中可能退化或丢失了；这些演化事件也产生了一些近似现代羽毛或者与现代羽毛完全相同的羽毛形态。非鸟恐龙身上的羽毛有一些现代羽毛具有的独特特征，但也有一些现生鸟羽没有的特征。尽管一些基于发育学资料建立的有关鸟类羽毛起源和早期演化的模型推测羽毛的起源是一个全新的演化事件，与爬行动物的鳞片无关，我们认为用来定义现代鸟羽的特征应该是逐步演化产生的，而不是突然出现。因此，对于羽毛演化而言，一个兼具逐步变化与完全创新的模型较为合理。从目前的证据推断，最早的羽毛既不是用来飞行也不是用来保暖，各种其他假说皆有可能，其中包括展示或者散热假说。展开整合性的研究有望为羽毛的起源问题提供更多思路。